I just recently did a fresh rebuild on my ls block and when the car got back to me it was doing 2 things. At idle it is misfiring and it is running rich. I changed the plugs and the wires are good. Please HELP! I think it is one of two things; Fuel Injectors took a crap or there is a vacuum leak. What is your take. Your $0.02 are always welcome.

 

Running rich is a byproduct of the misfire. When you have a misfire, the unburnt gas will cause the rich condition.
Solve the misfire problem and your rich condition should be resolved as well.
I would perform a compression test and a leak down test to determine the condition of the motor.
Also, what is timing set to? Is it obd 1 or 2? Any CEL?

 

Timing was set to stock. the timing is dead on. Its obd2. It has a CEL but i havent checked it. A compression test is not needed cause i just rebuilt the motor.

 

It cant be the timing cause it only misfires while idling. When i am coasting it runs fine.

 

Just because it's a fresh build doesn't mean squat. If you're assuming because it's a fresh build and nothing can go wrong, then you have a lot to learn. Did you rebuild the engine yourself? Did you do the install yourself?

 

No I didn't do it myself. I went to a professional shop. The guy said he has a gut feeling it's the injectors but I want some other feedback from other sources b4 I continue

 

Well first off, pull the CEL code, then get that fixed. If that doesn't solve your problem report back.

 

All right... i will do that. Let me get to autozone in bit

 

lol the cel is pretty much tellin you whats wrong...this aint the 60's anymore bro.
deff get back to us on that. i would say maybe a map sensor? you probably forgot to plug something in

 

I doubt it's an injector, otherwise you would have problems at all rpms, not just during idle.

 

that's the thing that has me confused... I had this problem problem before the rebuild. But i did not feel it as much. I think its because of the upped compression. I had this problem that i would be driving regularly and it would just like start to stumble on the RPM and go down and down until i mashed the gas pedal to the floor and then the car would jump. This problem would come like once in 2 weeks. So I dont want to leave the injector out just yet.

 

When was the last time you did an electronic tune up? New wires, cap, rotor, you may even have a faulty ignition coil. I had a similar problem when that contact spring on my ignition coil was bent and wasn't making good contact with the distributor. Car was slugish till I hit around 3400-3600 rpm, then the car would just pull.

 

my prelude did that after a rebuild when the valves didnt seat correctly just a thought and my 0.02

 

I was thinking as well about the valves.

 

BTW... this is what the computer said. Oxygen sensor, and random misfire in cylinders 1 2 and 4

 

Address the CEL that is listed first, fixing the first CEL Code may address the following codes if you're lucky.
Was a valve adjustment performed after the rebuild?

 

yea it was... I am talking with the guy to c what we are gonnna do.

 

thats what mine did too the machine shop ****ed me and only replaced 12 of the 16 valves they siad the other 4 were fine i even asked if ther were sure and 2 weeks later they tuliped

 

lol... that really sux bro.

 

my 91 is doing the exact same thing...except my fuel pressure is also 12lbs too low.
stumbles under a load...
fuel psi low...
runs rich...
kind of ironic huh?